1. Field of the Invention
The present invention relates to a particulate water absorbing agent having a water-absorbing resin as a main component. In particular, it relates to a particulate water absorbing agent having irregularly pulverized shape used for an absorbing substrate in a thin type diaper or a thin type sanitary napkin, which maintains conventionally not obtained thin state even after use and exerts superior absorbing ability.
2. Description of Related Art
At present, as component materials in sanitary articles such as a paper diaper, a sanitary napkin, so to speak an incontinence pad, and the like, a water-absorbing resin to absorb body fluid and hydrophilic fibers such as pulp are widely used. As the water-absorbing resin, for example, partially neutralized crosslinked polyacrylic acid, hydrolysates of starch-acrylic acid graft polymer, saponified vinyl acetate-acrylate copolymers, hydrolysates of acrylonitrile copolymer or acrylamide copolymers or crosslinked polymers thereof, crosslinked polymers of cationic monomers, and the like are used as main raw materials.
Water absorption characteristics conventionally required to the water-absorbing resin include superior liquid absorption capacity or water absorption speed, gel strength and gel permeability in contact with aqueous liquid such as body fluid, along with water suction force to suck water from a substrate containing aqueous liquid. Further, as recent trends, a water-absorbing resin powder with very narrow particle size distribution or a water-absorbing resin with high absorbency and low soluble content has been required and high absorbency against pressure or liquid permeability under pressure has essentially been required. Further, a water-absorbing resin superior also in handling, in addition to these improved performances has been required.
For example, there are many patent applications on many parameters specifying various properties of these water-absorbing resins or water absorbing agents with a water-absorbing resin as a main component, or on measurement methods thereof (US Reissued 32649, UK2267094B, U.S. Pat. Nos. 5,051,259, 5,419,956, 6,087,002, EP0629441, EP0707603, EP0712659, EP1029886, U.S. Pat. Nos. 5,462,972, 5,453,323, 5,797,893, 6,127,454, 6,184,433, 6,297,335, US Reissued 37021, U.S. Pat. Nos. 5,140,076, 6,414,214B1, 5,994,440, 6,444,744, 6,194,531, EP0940148, EP1153656, EP0605215, U.S. Pat. Nos. 5,147,343, 5,149,335, EP0532002, U.S. Pat. Nos. 5,601,452, 5,562,646, 5,669,894, 6,150,582, WO02/053198, EP0937739).
Water-absorbing resins superior in gel strength, soluble content and absorption capacity are proposed in US Reissued 32649. A water-absorbing resin superior in liquid permeability under no pressure, absorption speed and absorption capacity is proposed in UK2267094B. Technology specifying specific particle size distribution is also proposed in U.S. Pat. Nos. 5,051,259, 5,419,956, 6,087,002 and EP0629441. Further, a water-absorbing resin superior in absorbency against pressure under various loads or many measurement methods therefore are also proposed and water-absorbing resins with superior absorbency against pressure alone or in combination with other property are proposed in EP0707603, EP0712659, EP1029886, U.S. Pat. Nos. 5,462,972, 5,453,323, 5,797,893, 6,127,454, 6,184,433, 6,297,335 and US Reissued 37021.
Water-absorbing resins with little property decrease by impact are proposed in U.S. Pat. Nos. 5,140,076 and 6,414,214B1. A water-absorbing resin with specific powdery dust amount is proposed in U.S. Pat. No. 5,994,440, and a water-absorbing resin with less coloring is proposed in U.S. Pat. No. 6,444,744. Water-absorbing resins superior in gel durability in an aqueous L-ascorbic acid solution as index of urine resistance or superior in water absorption ability are proposed in U.S. Pat. No. 6,194,531 and EP0940148. A water-absorbing resin with superior air permeability is proposed in EP1153656. A water-absorbing resin with less residual monomers is proposed in EP0605215.
Further, in U.S. Pat. Nos. 5,147,343, 5,149,335, EP0532002, U.S. Pat. Nos. 5,601,452, 5,562,646, 5,669,894, water-absorbing resins with specific property are proposed as suitable to water absorbing articles such as a diaper having specific property, specific composition or specific polymer concentration.